The present invention relates to a unique overcenter hinge arrangement to be used with a microwave oven having an up-opening door. In microwave heating appliances, the nature of the heating phenomenon is that of stressing certain of the molecules of the product to be heated by using an electromagnetic field, commonly in the heating frequency range of 2450 MHz. One of the more serious problems with such microwave oven devices has been concern about radiation leakage and the resulting possibility of operator injury. The primary area of such radiation leakage is the periphery of the oven door and for this reason a number of door designs have been developed to limit this leakage.
One type of seal used to suppress leakage of microwave radiation is a capacitive seal, such as shown in U.S. Pat. No. 3,808,391. The seal plate disclosed therein is a thin metallic plate which covers the oven cavity and presses firmly against the edges of the cavity. The surface of the plate has a thin coating of a suitable dielectric organosol. Surrounding the capacitive seal is a conductive sealing ring which acts as a secondary seal. It is important when using a capacitive seal arrangement that there be as great a capacitance between the door seal plate and the oven cabinet as possible. For this reason it is important that the seal plate and the cabinet be kept clean and that the dielectric organosol coating not be scratched. An oven such as shown in the above cited U.S. patent which is hinged along a side edge can make use of such a capacitive seal with little chance of the seal plate becoming damaged or soiled.
Where it is desired to provide an oven with a cooking cavity which is extended in width so as to be able to cook simultaneously more than one item, however, a door hinged at its side edge is impractical because, when opened, too much of the area in front of the oven will be obstracted. An oven having a wide cooking cavity therefore requires either an up-opening or a down-opening door. An up-opening door is preferred with such an oven for two reasons. First, counter space in front of the oven is available for use both when the oven door is closed and when it is opened. Second, the operator will not be tempted to place items on the capacitive seal plate when loading and unloading the oven, as he would be in the case of a down-opening door. Thus the likelihood of damaging or soiling the seal plate is minimized. With an up-opening door arrangement, however, it is necessary that a mechanism be provided to aid in opening the door and holding the door in its open position to allow loading of the oven.